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Why did Facebook buy WhatsApp?

As reported by multiple news outlets, Koum also announced that WhatsApp now has 465 million monthly users and 330 million daily users. The latter is 15 million more than what was made public last week when Facebook announced the purchase.

Voice service will come first to Apple devices and Google's Android operating system, with Windows phones and Blackberry to follow.

The move puts WhatsApp in competition not only with other messaging apps that offer voice but chat tools such as Skype and even mobile carriers.WhatsApp's unlimited texting has already helped establish it in places where smartphones and fancy data plans are less common.

WhatsApp now has more than 330 million daily users and is popular in places such as India, South Korea and Germany.

It has 40 million users in India and another 38 million in Brazil, two countries highly coveted by tech companies such as Facebook for their large populations and emerging mobile customer base. WhatsApp hasn't released figures for the United States, where it is less popular.

Last week, Facebook shocked the business world when it announced it was buying WhatsApp for up to $19 billion in cash and stock -- by far the social network's largest acquisition to date.